Contributions to Invertebrate Palseontology. 529 



chambers about equalling the diameter of the uppermost of the five counted. 

 Siphon of moderate size, and in the specimen used slightly excentric. The 

 surface of the shell, so far as can be determined from the internal cast, has 

 been smooth. Perforations, or nodes representing them, large and elevated, 

 two to three times as long as wide, and occurring at every third septum below, 

 and at every second in the upper part of the specimen. 



Formation and Locality. — In limestone of the Upper Helderberg 

 group, at Smith and Price's quarry, near Columbus, Ohio. The 

 discovery and preservation of this peculiar specimen are due to the 

 careful observation of Mr. Edward Hyatt, of the State University, 

 at Columbus, Ohio. 



Genus GOMPHOCERAS Sowerby. 



Goiuplioceras Hyatti. 



Plate VIII, fig. 1, and Plate V, fig. 1. 



Gomphocerus Hyatti Whitf., Ann. N. Y. Acad. Sci., March, 1882, p. 206. 



Shell large and robust, slightly arcuate throughout, but more strongly 

 curved below than in the upper part ; somewhat rapidly expanding from below 

 upward to near the middle of the outer chamber, where it is suddenly con- 

 tracted to the aperture, and on the lateral margins again slightly expanding. 

 The rate of increase in diameter, as compared with the increased length, is 

 about as one and two, when measured on the inside curvature. Transverse 

 section of the shell obtusely subtriangular, flattened or but slightly convex on 

 the inner surface, rounded on the lateral surfaces, and obtusely rounded on the 

 back ; the dorso- ventral and lateral diameters are about as four and five, and 

 the triangular form is more perceptible in the earlier stages of growth, owing 

 to the greater convexity of the inner face in the upper portion and on the outer 

 chamber. Outer chamber comparatively short, being about two-thirds as high 

 as wide. Aperture large, irregularly tri-lobed, straight on the inner face, and 

 about four-fifths as wide as the entire width of the shell, and apparently about 

 two-thirds as wide in a dorso-ventral direction as laterally. The exact form 

 of the aperture on the outer side cannot be ascertained, owing to the imperfec- 

 tion of the specimen in this part. Septa moderately concave, very closely 

 arranged in the lower part, but more distantly disposed above ; the rate of in- 

 crease in distance somewhat gradual to near the upper portion, where two or 

 three of the septa are slightly more crowded. In the more distant portions, 

 three chambers occupy the space of one inch, but in the lower part of the 

 specimen, where the transverse diameter is a little more than one and a half 

 inches, they are less than one-twelfth of an inch apart. Sijihuncle of moderate 

 size and sub-centrally situated. Surface of the shell unknown. 



The specimen from which the description is taken is an internal 

 cast, not retaining any portion of the shelly structure ; but it ap- 



